The striatum is a complex neuroanatomical structure composed of at least two compartments called striasomal and matrix. There are currently no good molecular markers that distinguish between these subdivisions. It is clear that the striasomal neurons contain a higher abundance of u- opiate receptors than do the matrix compartment neurons. In this proposal the opiate responsiveness of the striatum will be characterized using a combination of electrophysiology and single cell molecular biology technique with particular attention paid to highlighting differences between the striasomal and matrix compartments. This is possible because of the anatomical precision of the techniques that will be employed. Initially dispersed rat striatal cells will be examined in a paradigm where opiates will be given acutely after which the opiate induced changes in electrophysiological responsiveness will be examined. In the same recording electrode we will have the reagents necessary to perform cDNA synthesis which will be followed by aRNA synthesis and expression profiling of several candidate genes. This analysis will yield a molecular fingerprint of the naive and opiate treated cells. The dispersed cell studies will be followed by examination of striatal cells in the live cortico-striatal slice preparation. In this paradigm the presence of synaptic connectivity will permit a determination of how chronic opiate treatment will alter the striatal responsiveness to afferent input from the cortex. Briefly, the cortex will be electrically stimulated while a recording electrode will be present in individual striatal cells which will be recorded from after which the mRNA contents analysed. Again the same experimental technology will be used. Finally, novel mRNAs whose abundance changes in response to opiates will be cloned and characterized from the dispersed cells in an effort to better understand the molecular differences in the physiological states of these cells due to opiate challenge. Additionally, this analysis may permit the characterization of striasomal and matrix specific markers. At the end of these studies the electrophysiological and molecular biological characterization of opiate responsive cells in the striatum will provide a molecular fingerprint of opiate responsiveness within striatal cells. This information will provide significant insight into how opiates modulate cellular physiology and may provide a framework in which it will be possible to modulate this responsiveness. Also, this detailed analysis of the striatum, with particular attention paid to the neuroanatomy of the structure, may provide insight into how the striatum is involved in different pathologies that affect the basal ganglia such as Parkinson's Disease and Huntington's Disease.